I would have to say for mulching you would want a longer edge but for regular discharging it shouldn't make much of a difference. I did a test for myself and sharpened my blades with the long edge, cut my lawn (with out hitting any sticks/roots) then took the blades off to see the condition of the edge. The first 2-3 inches had the most wear but down to about 4-5-6 inches of the edge showed signs of it cutting as well but not nearly as much as the tip of the blade. I would assume the longer edge also helps when going fast by reducing clippings a bit more.
I did this test because i had the same question only I have a blade sharpener and a bunch of blades. BTW I did this test on my 48" TTHP so it was done with 16" blades.

Matt, PLEASE tell me you were kidding about the 90 dollars for a set of blades!

As far as the question about the length of the edge, I believe the longer edge is going to have a few advantages, first, though it is no alot, there IS more cutting edge there. Now, just because there is say, for instance 30% more, that doesn't mean you're going to have 30% more mulching capability. The reason is, that as you get further into the center of the blade, you are losing speed. One BIG advantage of the long sharpening is though, is resistance. With a long sharpened bevel, there is no question that it will spin easier than a blunt thickness of a blade. I believe This can and does make a significant difference.

Joe

Thank you, Dad - for always being the dad that you were. You truly are my hero. You always were.

I don't think he is kidding on the blade price. I was quoted $26 each for factory Scag hi-lifts. I am presently trying a set of hi-lifts that I bought off mowtownusa on ebay for $7.50 each. So far, so good.